Polymerizable organopolysiloxane solutions and the process of preparing gels from these solutions



POLYMERIZABLE ORGANOPOLYSILOXANE SOLUTIONS AND THE PROCESS OF PRE-PARING GELS FROM THESE SOLUTIONS Alfred R. Gilbert, Schenectady, N. Y.,assignor to General Electric Company, a corporation of New York NoDrawing. Application May 11, 1954 Serial No. 429,136

12 Claims. or. 260-465) This invention relates to polymerizableorganopolysiloxane solutions comprising octamethylcyclotetrasiloxanecontaining from 0.05 to 20 percent, by weight, of a compound having theformula where X is a member selected from the class consisting ofhalogen, acyloxy radicals, and dimethyl sulfonium iodide radicals, andcatalytic amounts of a basic organopolysiloxane polymerization catalyst.This invention is also concerned with a process of preparingorganopolysiloxane gels which comprises effecting reaction between (1)octamethylcyclotetrasiloxane, (2) from 0.05 to 20 percent, by Weight, ofthe compound having the Formula I, and (3) catalytic amounts of a basicorganopolysiloxane polymerization catalyst.

Heretofore, organopolysiloxane gels have been prepared by polymerizingdiorganosiloxanes with suitable siloxane polymerization catalysts toform high molecular weight linear gums. These gums have then beenreacted with peroxides such as benzoyl peroxide to crosslink the linearchains to form gels. This method of forming gels is disadvantageous inthat the resulting gel contains the decomposition products of theperoxide. These decomposition products include, for example, acids andesters which tend to cause degradation of the final gel to a lowermolecular weight state upon use of the gel at high temperatures. Thus,when the peroxide crosslinking agent used is benzoyl peroxide, thedecomposition products include benzoic acid, p-phenylbenzoic acid, andphenylbenzoate. By the method of the present invention it is' possibleto form gels without the addition of these peroxide cross-linkingagents. By my method, gels may be formed by merely adding a compoundwithin the scope of Formula I to octamethylcyclotetrasiloxane whichcontains a basic organopolysiloxane polymerization catalyst. Uponheating the resulting solution, a crosslinked gel is formed which isfree of peroxide decomposition products.

Compounds within the scope of Formula I includechloromethylheptamethylcyclotetrasiloxane,iodomethylheptamethylcyclotetrasiloxane,heptamethylcyclotetrasiloxanylmethyl formate,acetoxymethylheptamethylcyclotetrasiloxane,propionoxymethylheptamethylcyclotetrasiloxane,dimethyl-(heptamethylcyclotetrasiloxanylmethyl)- sulfonium iodide, etc.Chloromethylheptamethylcyclotetrasiloxane is a well known compound andmay be prepared by passing chlorine gas throughoctamethylcyclotetrasiloxane and separating the former compound byfractional distillation of the product.Iodomethylheptamethylcyclotetrasiloxane may be prepared by refluxing amixture of chloromethylheptamethylcyclotetrasiloxane and sodium'iodidein acetone. The reaction products then may be added to water toprecipitate the halogenated organopolysiloxanes. Theiodomethylheptamethylcyclotetrasilox'ane may be isolated from theprecipitate by fractional distillation.

ice

Compounds within the scope of Formula I where X is an acyloxy radicalmay be prepared by heating a solution ofiodomethylheptamethylcyclotetrasiloxane and the silver salt of thedesired carboxylic acid in the acid itself. Thus,acetoxymethylheptamethylcyclotetrasiloxane may be prepared by the methodclaimed in my joint copending application with Simon W. Kantor, SerialNo. 429,133, filed concurrently herewith and assigned 'to the sameassignee as the present invention. This compound is prepared by heatinga mixture of iodomethylheptamethyb cyclotetrasiloxane and silver acetatein glacial acetic acid. The organopolysiloxanes may be separated fromthereaction mixture by pouring the reaction mixture into water andseparating the oily layer formed. Theacetoxymethylheptamethylcyclotetrasiloxane may be separated from thisoily layer by fractional distillation.

Dimethyl (heptamethylcyclotetrasiloxanylmethyl)- sulfonium iodide may beprepared from methyl-(heptamethylcyclotetrasiloxanylmethyl)-sulfide bymixing the latter compound with methyl iodide and allowing the mixtureto stand for several hours. The product may be purified by washing withpentane. Methyl-(heptamethylcyclotetrasiloxanyl)-sulfide may be preparedby the method disclosed in the application of Glenn D. Cooper, SerialNo. 349,099, filed April 15, 1953, Patent No. 2,719,165, and assigned tothe same assignee as the present invention. This method compriseseffecting reaction between chloromethylheptamethylcyclotetrasiloxane andsodium methyl mercaptide in absolute ethyl alcohol. The resultingsulfidemay be separated by adding the reaction products to water,separating the organic layer, and fractionally distilling this layer.

Under the action of a basic organopolysiloxane polymerization catalyst,the compounds within the scope of Formula I are believed to provide thecross-links necessary for the formation of gels by hydrolysis of the CHX radical, where X is as defined above, to form a compound made up oftwo cyclic portions joined by a silicon-oxygen-silicon linkage. Thiscompound has the probable structure 11 CH3 CH3 Concurrent with'theformation of compound (II), the basic organopolysiloxane polymerizationcatalyst also is believed to rupture a silicon-oxygen linkage in each ofthe cyclic portions of compound (II) and also to rupture correspondinglinkages in octamethylcyclotetrasiloxane with which the compound withinthe scope of Formula I is mixed. This results in a mixture ofshort-chain linear and short-chain cross-linked dimethyl siloxanes whichare condensed to form a high molecular weight gel which is cross-linkedby silicon-oxygen-silicon bonds.

As stated above, the concentration of compounds within the scope ofFormula I may vary from about 0.05 percent to 20 percent, by weight, ofthe octamethylcyclotetrasiloxane present. The amount of compound (I)included controls the properties of the final gel. For example,

where low concentrations of compound (I) are used, the

Patented Jan. 6, 1959' mean an amount of catalyst sutlicient to causepolymerization of the low molecular weight organopolysiloxane solutronof the present invention to a high molecular weight organopolysiloxane.In general, from about 0.001 to 0.5 percent, by weight, ofpolymerization catalyst has been found to be effective; Among the basiccatalysts which may be used in the present invention are included themetal hydroxide catalysts such as potassium hydroxide and cesiumhydroxide. Also included are the transient organopolysiloxanepolymerization catalysts such as the solid quaternary ammonium hydroxidecatalysts disclosed in the copending application of Simon W. Kantor,Serial No. 429,132, now abandoned, filed concurrently herewith andassigned to the same assignee as the present invention. These solidquaternary ammonium hydroxide catalysts are solid tetramethyl ammoniumhydroxide and solid benzyl trimethyl ammonium hydroxide. Other suitabletransient catalysts are the quaternary phosphonium catalysts disclosedin my joint copending application with Simon W. Kantor, Serial No.429,134, now abandoned, filed concurrently herewith and assigned to thesame assignee as the present invention. These quaternary phosphonium,catalysts include tetra-n-butyl phosphonium hydroxide, butyltricyclohexyl phosphonium hydroxide, tetraethyl phosphonium hydroxide,tetra-n-butyl phosphonium butoxide, etc. These quaternary phosphoniumcatalysts may be used as their concentrated aqueous solutions orconcentrated organopolysiloxane solutions. I prefer to use thesetransient quaternary ammonium and quaternary phosphonium catalysts inthe process of the present invention since these catalysts aredecomposable upon heating to temperatures above about 130 C. Thus, a gelmay be formed using these catalysts by the method of the presentinvention, and after the formation of the gel the catalyst may bedecomposed. Gels formed from these transient catalysts retain their goodphysical and electrical properties for extended periods of time attemperatures as high as 250 C., while gels formed from the metalhydroxide catalysts revert to a lower molecular weight state upon beingheated to these high temperatures.

The polymerizable organopolysiloxane solutions of the present inventionmaybe prepared in a variety of ways. For example, a compound within thescope of Formula I may be added to octamethylcyclotetrasiloxane and acatalyst may then be added to the resulting solution. If desired, thecatalyst may be added to the octarnethylcyclotetrasiloxane first withthe later addition of the compound (I). Where it is desirable to use asolution of chloromethylheptamethylcyclotetrasiloxane inoctamethylcyclotetrasiloxane, the solution may be prepared by passing asufiicient amount of chlorine gas through the latter compound to'formthe desired concentration of the chlorinated compound and the hydrogenchloride formed during the reaction may be removed by any suitable meanssuch as, for example, by washing the solution with water, by passing astream of inert gas through the solution, or by subjecting the solutionto a vacuum. After the hydrogen chloride has been removed from thesolution, the basic organopolysiloxane polymerization catalyst may beadded to the solution in the desired amount to form thepolymerizable'organopolysiloxane solution of the present invention.

Where the gels prepared by the method of the present invention are to beused as potting gels in electrical apparatus it is desirable toobtain agel containing no air bubbles." Since octamethylcyclotetrasiloxanesometimes contains'some dissolved air which could lead to the formationof bubbles in the final gel, it is desirable to subject this compound toa vacuum to remove'this air. This air may be evacuated before compound(I) or the catalysts are added or after either or both of theseingredients are added. After the removal of'dis solved air it ispreferable to place the evacuated product under a nitrogen atmosphere toprevent the solution of additional oxygen. It should be understood thatsatisfactory gels may be formed by the method of the present inventionwithout the removal of dissolved air from the octamethylcyclotetrapolymerization takes place. The temperature and time of polymerizationdepend on the particular polymerization catalyst used. For example, whenusing potassium hydroxide as the polymerization catalyst, thetemperature of the reaction usually varies from about 145160 C. Whenusing cesium hydroxide, the temperature polymerization ranges from about110150 C. When using quaternary ammonium hydroxides, the temperaturerange is from about -130 C. When using a quaternary phosphoniumcatalyst, the temperature of polymerization may vary from about roomtemperature up to about 130 C. The time required for polymerization tobe com' pleted is shortest at the upper limits of the temperature rangesfor the various catalysts. Thus, when using potassium hydroxide at atemperature near 160 C., polymerization is completed in two to threehours. When using either the quaternary ammonium or quaternary phosphonium catalysts at temperatures from about 110-130 C., thepolymerization is completed in several minutes. When using a quaternaryammonium or quaternary phosphonium catalyst, it is essential to maintainthe polymerization temperature below about 130 C., the temperature atwhich these catalysts decompose. After the formation of a gel usingthese catalysts, it is desirable to heat the gel to a temperature aboveabout 130 C. for times up to about one hour to cause decomposition ofthe polymerization catalyst.

The following examples are illustrative of the practice of my inventionand are not intended for purposes of limitation.

Example 1 A tetra-n-butyl phosphonium hydroxide catalyst was prepared bymixing 6 cc. of an aqueous solution of tetran-butyl phosphoniumhydroxide, containing 51 mg. of the hydroxide per cc. of solution, withgrams of octamethylcyclotetrasiloxane. Themixture was evacuated at about2 microns for two and one-half hours. sulted in a homogeneous clearsolution containing 43.5 mg; oftetra-n-butyl phosphonium'hydroxide percc. A catalyzed solution of octamethylcyclotetrasiloxane was thenprepared by mixing 1.3 ml.1of this catalyst solution with 191 grams ofthe former compound. A polymerizable solution was then formed by adding0.2 gram of chloromethylheptamethylcyclotetrasiloxane to 47.8 grams ofthe catalyzed ,octamethylcyclotetrasiloxane solution.

Twenty ml. of this latter solution was placed in a test 7 tube andevacuated for five minutes at 1 mm. to remove any dissolved air. Drynitrogen was added to return the system to one atmosphere and the samplewas heated for ten minutes at C. At the end of this timea Example 2 7 Asecond solution of chloromethylheptamethylcyclotetrasiloxane incatalyzed octamethylcyclotetrasiloxane was prepared by adding 0.05 gramof the former com.- pound to 47.8 grams of the catalyzedoctamethylcyclotetrasiloxane solution prepared in Example 1.

This re This gel Byhe method of Example 1 this solution was evacuatedfor five minutes at 1 mm. to remove any dissolved air-and dry nitrogenwas added to return the system to one atmosphere. The sample was thenheated for ten minutes at 110 C. to form a firm cross-linked, tolueneinsoluble gel.

Example 3 A solution of 50 grams of octamethylcyclotetrasiloxane and 0.5gram of chloromethylheptamethylcyclotetrasiloxane were placed in abeaker and heated to 110 C. At this time approximately 0.1 gram of solidtetramethyl ammionium hydroxide containing about 25 percent, by weight,water of crystallization was added and the solution was maintainedbetween 110 and 120 C. for five minutes. At the end of this time a stillcross-linked, toluene insoluble gel had formed.

Example 4 A polymerizable solution was prepared by mixing 0.1 gram ofacetoxymethylheptamethylcyclotetrasiloxane with 47.8 grams of thecatalyzed octamethylcyclotetrasiloxane solution of Example 1. Theacetoxymethylheptamethylcyclotetrasiloxane had been prepared by themethod described in my joint copending application referred to above,Serial No. 429,133, which is hereby incorporated by reference into thepresent Example. This solution was evacuated for five minutes at 1 mm.and returned to one atmosphere by allowing nitrogen to enter the system.The solution was then heated for ten minutes at 110 C. to form a firmcross-linked gel which was insoluble in toluene.

Example 5 Methyl-(heptamethylcyclotetrasiloxanylmethyl-(sulfide wasprepared by adding 330 grams (1.0 mole) ofchloromethylheptamethylcyclotetrasiloxane to a solution of 1.0 mole ofsodium methyl mercaptide in 500 ml. of absolute alcohol. The solutionwas cooled in an ice bath and stirred for four hours. Two liters ofwater were then added and the organic layer which was formed wasseparated, washed with water, and dried over calcuim chloride. The puresulfide was obtained by fractional distillation. Dimethyl(heptamethylcyclotetrasiloxanyl) sul- -fonium iodide was formed frommethyl-(heptamethylcyclotetrasiloxanylmethyl)-sulfide by mixing 7.0grams of the latter compound with 5.7 grams of methyl iodide andallowing the mixture to stand overnight in the dark. This resulted in acrystalline mass which was filtered and washed several times withpentane to yield pure dimethyl-(heptamethylcyclotetrasiloxanylmethyl)-sulfonium iodide. A polymerizablesolution was then formed by adding 0.1 gram ofdimethyl-(heptamethylcyclotetrasiloxanylmethy1)-sulfonium iodide to 47.8grams of the catalyzed octamethylcyclotetrasiloxane solution prepared inExample 1. This solution was then evacuated for five minutes at 1 mm. toremove dissolved air and brought back to atmospheric pressure by theintroduction of nitrogen. The solution was then heated at 110 C. for tenminutes to form a stiff, cross-linked gel which was insoluble intoluene.

Although the present invention has been described with reference to asolution of compounds within the scope of Formula I inoctamethylcyclotetrasiloxane containing a basic organopolysiloxanepolymerization catalyst, it should be understood that other cyclicdimethyl siloxanes or dialkyl silanes or diaryl silanes such as, forexample, the trimer, or pentamer, or octamer of dimethylsiloxane, cyclicdiethylsiloxanes, cyclic diphenyl siloxanes, cyclic methylethylsiloxanes, cyclic methylphenyl siloxanes, etc., may be substituted forthe octamethylcyclotetrasiloxane.

The gels formed from the polymerizable organopolysiloxane solutions bythe method of the present invention are useful as potting gels inelectrical apparatus. For example, the gels of the present invention maybe formed inside of tr'ansformersand the like to function as insulatingand dielectric materials.

What I claim as new and desired to secure by Letters Patent of theUnited States is:

1. An organopolysiloxane solution polymerizable to a cross-linked gelconsisting of octamethylcyclotetrasiloxane containing from 0.05 to 20percent, by weight, based on the weight of saidoctamethylcyclotetrasiloxane, of a compound having the formula where Xis a member selected from the class consisting of halogen, acyloxyradicals, and dimethyl sulfonium iodide radicals, and a catalytic amountof a basic organopolysiloxane polymerization catalyst.

2. An organopolysiloxane solution polymerizable to a cross-linked gelconsisting of octamethylcyclotetrasiloxane containing from 0.5 to 20percent, by weight, based on the weight of saidoctamethylcyclotetrasiloxane, ofchloromethylheptamethylcyclotetrasiloxane and a catalytic amount of abasic organopolysiloxane polymerization catalyst.

3. An organopolysiloxane solution polymerizable to a cross-linked gelconsisting of octamethylcyclotetrasiloxane containing from 0.05 to 20percent, by weight, based on the weight of saidoctamethylcyclotetrasiloxane, ofacetoxymethylheptamethylcyclotetrasiloxane and a catalytic amount of abasic organopolysiloxane polymerization catalyst.

4. An organopolysiloxane solution polymerizable to a cross-linked gelconsisting of octamethylcyclotetrasiloxane containing from 0.05 to 20percent, by weight, based on the weight of saidoctamethylcyclotetrasiloxane, of dimethyl(heptamethylcyclotetrasiloxanylmethyl)-sulfonium iodide and a catalyticamount of a basic organopolysiloxane polymerization catalyst.

5. An organopolysiloxane solution polymerizable to a cross-linked gelconsisting of octamethylcycloeterasiloxane containing from 0.05 to 20percent, by weight, based on the weight of saidoctamethylcyclotetrasiloxane, of a compound having the formula where Xis a member selected from the class consisting of halogen, acyloxyradicals, and dimethyl sulfonium iodide radicals, and from 0.001 to 0.5percent, by weight, of tetra-n-butyl phosphonium hydroxide.

6. An organopolysiloxane solution polymerizable to a cross-linked gelconsisting of octamethylcyclotetrasiloxane containing from 0.05 to 20percent, by weight, based on the weight of saidoctamethylcyclotetrasiloxane, of a compound having the formula Iogcmhsropsucnoomx where X is a member selected from the class consistingof halogen, acyloxy radicals, and dimethyl sulfonium iodide radicals,and from 0.001 to 0.5 percent, by weight, of solid tetramethyl ammoniumhydroxide.

7. The process of preparing a cross-linked organopolysiloxane gel whichcomprises mixing and heating (1) octamethylcyclotetrasiloxane, (2) from0.05 to 20 percent, by weight, based on the weight of said octamethyl.cyclotetrasiloxane, of a compound having the formula louomnsiopslnonnomx where X is a member selected from the classconsisting of halogen, acyloxy radicals, and dimethyl sulfoniurn iodideradicals, and (3) a catalytic amount of a basic organopolysiloxanepolymerization catalyst.

8. The process of preparing a cross-linked organopolysiloxane gel whichcomprises mixing and heating 1) octamethylcyclotetrasiloxane, (2) from0.05 to 20 percent, by weight, based on'the weight of said octarnethyl-vcyclotetrasiloxane, of chloromethylheptamethylcyclotetra siloxane, and(3) a catalytic amount of a basic'organopolysiloxane polymerizationcatalyst.

9. The process of preparing a cross-linked organopolysiloxane gel whichcomprises mixing and heating (1) octamethylcyclotetrasiloxane, (2)from0.05 to 20 percent, by weight, based on the weight of saidoctamethylcyclotetrasiloxane, ofacetoxymethylheptamethylcyclotetrasiloxane, and (3) a catalytic amountof a basic organopolysiloxane polymerization catalyst.

10. The process of preparing a cross-linked organopolysiloxane gel whichcomprises mixing and heating (1) octamethylcyclotetrasiloxane, (2) from0.05 to 20 percent, by weight, based on the weight of saidoctarnethylcyclotetrasiloxane, of dimethyl(heptamethyleyclotetrasiloxanylmethyl)-sulfonium iodide, and (3) acatalytic amount of a basic organopolysiloxane polymerization catalyst.

11. The process of preparing a cross-linked organ0-,

polysiloxane gel which comprises mixing and heating (1)octamethylcyclotetrasiloxane, (2) from 0.05 to 20 percent, by weight,based on the weight of said octamethylcyclotetrasiloxane, of a compoundhaving the formula where X is a member selected from the classconsisting of halogen,-acyloxy' radicals, and dimethyl sulfonium iodideradicals, and (3) from- 0.001 to-0.5 percenhby weight, of tetra-n-butylphosphonium hydroxide:

12. The process of preparing a cross-linkedorganopolysiloxane gel whichcomprises mixing and heating (1) octamethylcyclotetrasiloxane, (2) from0.05 to 20 percent, by weight, based on the weight of saidoctarnethylcyclotetraslioxane, of a compound having the formula oucnmsiosuons 032x where X is a member selected from the class consisting. ofhalogen, acyloxy radicals, and dimethyl sulfonium, iodide'radicals, and(3) from 0.001 to 0.5 percent,vby weight, of solid tetramethyl ammoniumhydroxide.

References Cited in the file of this patent UNITED STATES PATENTS

1. AN ORGANOPOLYSILOXANE SOLUTION POLYMERIZABLE TO A CROSS-LINKED GELCONSISTING OF OCTAMETHYLCYCLOTETRASILOXANE CONTAINING FROM 0.05 TO 20PERCENT, BY WEIGHT, BASED ON THE WEIGHT OF SAIDOCTAMETHYLCYCLOTETRASILOXANE, OF A COMPOUND HAVING THE FORMULA